An electrochemical oxygen sensor with a noble metal/air electrode as a reference electrode has been known from DE 42 31 256 C2. This oxygen sensor operates according to the principle of the "oxygen pump" and has a very long service life, because no sacrificial anode is consumed, as it is known from galvanic measuring cells. Oxygen is released at an auxiliary electrode, which is frequently also called a counterelectrode. The oxygen released at the auxiliary electrode may interfere with both the reference electrode and the measuring electrode. The interaction with the measuring electrode is especially disturbing, because excessively high oxygen contents may be mimicked. The auxiliary electrode is therefore arranged away from the measuring electrode, namely, behind the reference electrode, in the prior-art oxygen sensor.
However, it has been found that this measure alone is not sufficient, because if the oxygen sensor is moved, e.g., in portable measuring devices, electrolyte solution rich in oxygen, due to the change in position suddenly reaches the measuring and reference electrodes and thus it directly or indirectly causes a change in the electrode signal. In addition, the resistance of the electrolyte between the electrodes changes during the movement of the oxygen sensor, because the sensor is usually filled with electrolyte only partially, which may lead to potential variations especially at the measuring electrode.